The invention relates to an apparatus in spinning preparation for separating foreign objects at conveying equipment for fibre material, for example, cotton, synthetic fibres or the like.
It is known to provide a device for separating the foreign objects associated with the conveying equipment, which device comprises an arrangement for producing a current of blast air that flows in the direction onto the conveying equipment and generates an air stream that detaches the foreign objects from the conveying equipment and carries the foreign objects away, the arrangement comprising a plurality of blast nozzles that are arranged across the width of the conveying equipment and are connected to a compressed air pipe and to valves.
From WO 89/01832 A it is known that a plurality of blast nozzles are arranged across the width at an outer wall of the pneumatic conveyor conduit through which a current of fibre and air flows. The blast nozzles are placed freely side by side on the wall and are spaced relative to one another. Eight blast nozzles are intended to be sufficient for a 160 mm wide conveyor conduit. In order to emit gas bursts, air valves having a response time of 10 msec or less are associated with the blast nozzles. In practice, the nozzles with the valves are fixed to the outer wall of the conveyor conduit. These valves, which are arranged side by side, require a good deal of space. This results in relatively large distances between the blast nozzles, with a consequent considerable dispersion of the blast air jets. The blast air is thus effective over relatively wide areas, which leads to an undesirably high separation of good fibres with the foreign objects.
In the case of a known apparatus (DE-A-196 45 844), two slow-speed feed rolls are associated with an opening roll laterally and horizontally and feed the fibre material to the opening roll. To keep the co-rotating envelope of air on the opening roll, guide plates are provided. At the lower end of the opening roll there is a device (sensors) for optical detection of foreign particles in the fibre tufts, which is located in a collecting area for separated particles. Between the guide plate and a blade there is an opening though which a current of blast air is directed obliquely from below briefly onto that area of the roll surface where the fibre tufts contain unwanted foreign particles. In this way, the contaminated fibre tufts are blown off the roll surface and then carried away. The drawback of this apparatus is the considerable space requirement, which is caused inter alia by the blowing direction of the blast air source (air nozzles) in the area beneath the opening roll. In addition, it is inconvenient that the blast air source and the valves are located freely in the waste collecting area, which leads to considerable interference to operation, interruptions and the like. Another disadvantage is that the air nozzles with the magnetic valves are arranged separately across the width of the roll. The air jet of each individual air nozzle is therefore directed either tangentially, or slightly away from this tangent, away from the opening roll. A consistent quality of separation and a rapid adjustment when the processed fibre material is changed to one with different proportions of foreign objects is not possible with this apparatus. Finally, the air nozzles are in the form of flat fan nozzles, so that with not too large a number of nozzles it is possible to cover the entire width of the roll.